织梦dedecms自定义表单中加入验证码

<input name="validate" type="text" id="vdcode" style="text-transform:uppercase;" size="8"/> <img id="vdimgck" align="absmiddle" onClick="this.src=this.src+'?'" style="cursor: pointer;" alt="看不清？点击更换" src="../include/vdimgck.php"/>  <a href="javascript:vide(-1);" onClick="changeAuthCode();">看不清？ </a>

<script type="text/javascript" language="javascript">//验证码 function changeAuthCode() {     var num =     new Date().getTime();    var rand = Math.round(Math.random() * 10000);    num = num + rand;    $('#ver_code').css('visibility','visible');    if ($("#vdimgck")[0]) {        $("#vdimgck")[0].src = "../include/vdimgck.php?tag=" + num;  }    return false;    }</script>

if(!empty($dede_fields))       {        $validate = empty($validate) ? '' : strtolower(trim($validate));            $svali = strtolower(GetCkVdValue());                            if(($validate=='' || $validate != $svali) && preg_match("/6/",$safe_gdopen)){                ResetVdValue();                ShowMsg('验证码不正确!',$dede_add,0,1000);                exit;            }       }